The present matrix balancing fixture, or apparatus for centering a test article in a carrier box relates to the universal type gauge covered in and disclosed in my prior U.S. Pat. No. 2,964,850 and to the universal type gauge frame shown therein. The present invention more specifically relates to and is an improvement upon the apparatus for centering articles in a matrix shown in my prior U.S. Pat. No. 2,999,282. In such prior matrix centering device or article, a carrier box for a test specimen was provided and slidable gauge templates are operably positioned by carrier cartridges mounted on support posts forming a part of the gauge frame or apparatus. These cartridges slidably and operatively position templates that can be moved laterally inwardly toward each other in horizontal planes for engaging a test article at spaced vertical portions thereof. The apparatus also positions an open ended box on a vertical axis so that the test article can extend therethrough and when the article is properly positioned in the receiving box, suitable embedment material or matrix carrier forming material is poured around the test article in the box to solidify in place to embed or position the test article in a given relationship to the carrier box and accurately formed margins thereof. In my prior apparatus, indicators or gauges are provided at several vertical spaced portions of the apparatus for reading and accurately indicating the position or size of the test specimen in the gauge. However, these indicators extended outwardly appreciably from the gauge apparatus and they were difficult to read as upper and lower indicators were provided at opposed lateral margins of the article centering apparatus.